The present invention relates to sterilization of products, and more particularly to sterilization of products using pulsed, short duration, polychromatic, incoherent light. Even more particularly, the present invention relates to sterilization of products wherein a transmissive carrier is employed to transport the product through a treatment zone thereby permitting complete sterilization of the product by avoiding shadowing of the pulsed polychromatic incoherent light.
The present invention addresses the particular need which exists for improved methods and apparatus for efficiently sterilizing or reducing the microbiological burden on the surfaces of or throughout the volume of anything requiring sterilization. Examples of surfaces and volumes of products needing sterilization include surfaces of solids and/or solids within liquid products, surfaces or volumes of food stuffs, surfaces or volumes of containers for food stuffs, surfaces of medical devices, surfaces of packages, and volumes of liquids.
By way of example, any varieties of foods (such as fresh fish) and medical products, have a relatively limited storage time before being subject to microbial and/or enzymatic spoilage, which limits the distribution and marketing. Further in the case of medical products, in particular, microbial deactivation must be achieved to medically acceptable sterility levels. Improved methods and apparatus suitable for extending the shelf life of perishable foods, medical devices and any other products requiring sterilization are therefore desirable.
Improved methods and apparatus for reducing or eliminating biological activity without degradation or other undesirable secondary effects on the product is also desirable.
An improved apparatus and method for sterilization of non-food products such as medical devices, is particularly desirable for research apparatus such as chemical reagents, plates, and test tubes which must be sterile to be used in unlimited medical or research procedures.
The-photo biological effects of light, including visible light (380-780 nm), near ultraviolet light (300-380 nm) and far ultraviolet light (190-300 nm), have been studied for many years, for example, as reported in Jagger, J., xe2x80x9cIntroduction to Research in Ultraviolet Photo Biologyxe2x80x9d, Prentice Hall, Inc., 1967, and efforts have been made to employ light for sterilization.
U.S. Pat. No. 5,034,235 (hereinafter the ""235 patent, issued Jul. 23, 1991 to Dunn, et al.) incorporated herein by reference, teaches utilizing intense, short duration pulses of UV-rich polychromatic, incoherent light in order to sterilize a surface of a food product.
Problematically, the use of pulsed light for sterilization of a product surface (typically meaning an exterior solid surface thickness to about 0.1 mm) is only as effective as the ability of the pulsed light to penetrate through any obstructions to the surfaces or volumes to be sterilized, that is, all areas to be treated must be fully contacted by the sterilizing levels of light.
This means, for example, that if the target object is a fluid, a fluid having a higher degree of transparency to a broad range of wavelengths, such as water and air, the target object will be more effectively treated by a given level of light than a more opaque fluid such as wine or sugar solution. A more opaque fluid solution would require either a smaller treating volume or a higher level of light, both of which reduce efficiency and in the later case, risk damage to the target object by the sterilizing level of light. Similarly, if the target object is a solid object or material, such as a food product or medical device, the solid object must be contacted by the pulsed light sufficiently, on all surfaces, to be sterilized, without shadowing of any such surfaces.
U.S. Pat. No. 4,871,559 (hereinafter the ""559 patent, issued Oct. 3, 1989 to Dunn et al.), incorporated herein by reference, teaches that certain solid materials such as cut, sliced or particulate foods (e.g., dried vegetables) may be treated in a fluid suspension medium in order to avoid shadowing effects. However, this method obviously is limited, in its usefulness, to those products that may be processed and suspended in fluid.
With respect to solid objects such as a container being treated by pulsed light, the ""559 patent teaches that such an object may be treated by rotating or turning the object during a multiple exposure treatment involving a series of light pulses; or by letting the object freely fall through a treatment zone surrounded by flashlamps so that substantially the entire surface of the product is subjected to simultaneous treatment.
The ""559 patent also teaches that the solid object or material may be packaged in a transparent wrapping material prior to the pulsed light treatment to reduce the shadowing effect as compared to a more opaque wrapping material used around the solid object.
U.S. Pat. No. 5,489,442 (hereinafter the ""442 patent, issued Feb. 6, 1996 to Dunn, et. al.), incorporated herein by reference, similarly teaches methods for treatment of solid objects. In particular, the ""442 patent describes the use of rollers or shakers to rotate the product between two or more flashes, or that the product may be rotated manually.
Unfortunately, these prior art methods of rotating the solid product or material, (such as a container or wrapped package), while sterilizing, can be ineffective unless a large number of pulses are used while the solid product is moving within the treatment area (or treatment zone) to allow all of its surfaces to be exposed to the sterilizing light. Meanwhile, some of the sterilizing light will be wasted on opaque surfaces shadowing the product to be sterilized. Consequently, a lesser throughput capacity results and cost, energy and time parameters are increased.
Thus, it is desirable to have a method and apparatus for transporting a solid product through a treatment zone of a sterilization chamber without the need for product manipulation within the zone or for multiple treatment exposures, such that a higher throughput capacity is thereby achieved, while decreasing the cost, time and energy required for the sterilization.
The present invention advantageously addresses the above and other needs by providing a method and apparatus for sterilizing a product with pulsed light while avoiding shadowing of the pulsed light upon the product being sterilized.
U.S. application Ser. No. 09/326,168, filed Jun. 4, 1999 of Clark, et al., for PARAMETRIC CONTROL IN PULSED LIGHT STERILIZATION, U.S. application Ser. No. 08/846,102 of Clark, et al., for PARAMETRIC CONTROL IN PULSED LIGHT STERILIZATION, now U.S. Pat. No. 5,925,885, and U.S. application Ser. No. 08/651,275, of Clark, et al., for STERILIZATION OF PACKAGES AND THEIR CONTENTS USING HIGH-INTENSITY, SHORT-DURATION PULSES OF INCOHERENT, POLYCHROMATIC LIGHT IN A BROAD SPECTRUM, now U.S. Pat. No. 5,786,598, are all incorporated herein by reference.
The present invention advantageously addresses the needs above as well as other needs by providing an apparatus for transporting a target object within a pulsed light sterilization chamber via a transmissive carrier which allows for sterilization of the target object without obstruction or shadowing by the transmissive carrier. The present invention also provides for a system for sterilizing the target object using such transmissive carrier to transport the target object through the system.
One embodiment of the invention is characterized as an apparatus for carrying a target object having a surface, within a pulsed light sterilization chamber within which pulsed sterilizing light is emitted. The apparatus comprises: a transmissive carrier within the treatment zone, the transmissive carrier engaging the target object, the transmissive carrier having a transmissivity of at least about 10% between 250 and 350 nm wavelength; and moving means coupled to the transmissive carrier for moving the target object by moving the transmissive carrier through the treatment zone, the surface being sterilized by the pulsed sterilizing light, at least a portion of the pulsed sterilizing light passing through the transmissive carrier before reaching the target object.
In another embodiment, the invention may be characterized as a system for sterilizing a target object having a surface. The system comprises: a pulsed light sterilization chamber comprising a treatment zone and means for emitting pulsed sterilizing light within the treatment zone; a moving means; and a transmissive carrier within the treatment zone, the transmissive carrier engaging the target object, and being coupled to the moving means, the moving means moving the target object by moving the transmissive carrier through the treatment zone such that the surface of the target object is sterilized by the pulsed light in the treatment zone, at least a portion of the pulsed light passing through the transmissive carrier before reaching the target object.